When medicine hits the reality gap

Medicine often comes up with great ideas that fall down a little in practice. Continuous Positive Airways Pressure, or CPAP, is one of these – a mask that can essentially undo the effects of obstructive sleep apnoea, but not if it spends the night hanging from the bedpost after the patient decides it’s unbearably tight.

Orthotic devices and splints suffer similar fates – diligently worn to appointments, only to be discarded as soon as the patient gets home. Elastic stockings can help prevent deep-vein thrombosis (DVT), but not when sported on their comfiest setting (rolled down loosely round the ankles). And a recent illustration of this gap between ideal medicine and disappointing reality is the new strategy for measuring blood pressure: ambulatory blood pressure monitoring, or ABPM.

It has been known for a long time that measuring blood pressure in clinics can give an unreliable picture of people’s blood pressure when they’re out in the world. Blood pressure varies day and night according to what you’re doing; it’s meant to vary, to help you meet the demands on your heart. What matters for your long-term health is the average – that is, whether you’re “running high” overall. A clinic reading is a one-off, reflecting the situation at that moment in time. And it may be falsely inflated by several factors. You may have rushed to the appointment; it may be at a different time of day from the last time you were measured; you may offer your left arm when last time you used your right (blood pressure can vary slightly between arms). Many people suffer from “white-coat hypertension”, where their blood pressure goes up at the sight of a doctor (in what may be a lesson for doctors, this effect is less pronounced when the reading is taken by a nurse).

In an attempt to address this problem, the seeming genius of ambulatory monitoring was invented. The new national guidelines on hypertension – published in 2011 – state that ABPM should be used to confirm a suspected diagnosis of hypertension, which sounds great in theory. In practice, it has a few drawbacks. In ambulatory monitoring, you wear a blood pressure cuff night and day for a 24-hour period. The cuff inflates and deflates every 20 minutes or so during the day and hourly – or thereabouts – overnight. This gives a much more reliable picture of what your blood pressure is doing over a period of time.

Unfortunately – this is evidence drawn from anecdote rather than a double-blind controlled trial – it is unpopular among patients. The cuff, one elderly lady told me, “grabs your arm in a death-grip”. Another patient documented his trial overnight: every time his cuff inflated he texted his wife (who was staying elsewhere) to let her know he’d woken up again.

One of my colleagues took the system home with her, reasoning that you shouldn’t inflict on patients something you’re not willing to put up with yourself.

I wondered how her experiment had gone. “It wasn’t too bad,” she reported. “Even at night?” “Oh, I took it off at night. You wouldn’t be able to sleep,” she said.

As a doctor, you get good at explaining to patients how beneficial various investigations and treatments are. But it’s vital to consider if they’re also annoying. Drugs that have to be taken at odd times of day, cream that feels nasty, anything that involves pain or laborious attention to detail are all prone to failure. And you may never know why, as patients are often kind enough to keep such minor irritations from you.

Sophie Harrison is a hospital doctor in South Yorkshire

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